1. Field of the Invention
This invention relates, in general, to means for initiating an electrical signal within an otherwise-inaccessible region by the manipulation of a shaft passing into the region, and in particular, to an electronic dial combination lock.
2. Description of the Related Art
There is an ongoing need for means for authorized personnel to access otherwise-inaccessible security regions easily, such as are found in safes, lock-boxes, storage rooms and the like. One such means is the well-known combination lock which typically comprises a plurality of tumbler wheels coaxially journalled on a rotating spindle which projects outwardly from the lock and is manipulated within one degree of freedom (rotational) through a predetermined, sequential series of rotations to operate a bolt within the lock. A variation on such a lock is discussed in U.S. Pat. No. 3,968,667.
With the advent of miniaturized components and digital logic circuitry, the art has seen an increasing requirement for means for producing sequential signals which may be utilized as a means for unlocking a protected region. One such sequential switch means having two degrees of movement is disclosed in my U.S. Pat. No. 3,758,734, while a second such means is illustrated in my U.S. Pat. No. 3,702,070.
An electronic combination lock which utilizes a sequential signal producing means having one degree of movement to actuate a bolt to unlock a door is disclosed in U.S. Pat. No. 4,038,846 to Klann.
These prior art devices share certain drawbacks: Some of the electronics for initiating the electrical signal are mounted externally of the protected region, and hence, are subject to a greater degree of tampering by unauthorized personnel.
A second drawback is that they are not easily adapted to retrofit existing security regions which utilize conventional, mechanical combination locks for electrical actuation.